Microsoft released Windows 10 Mobile build 10586.122 today. Along with a list of fixes, they dropped some big hints that this will likely be the build that non-Insiders receive upon upgrading to Windows 10 Mobile from Windows Phone 8.1.
If you’re a Windows Insider who is willing to help test the upgrade path that most customers will be taking from Windows Phone 8.1 – you can use the Windows Device Recovery Tool to go back to Windows Phone 8.1 and then download the Windows Insider app from the Store and jump into either the Slow or Release Preview rings to pick up Build 10586.122 for your phone. Make sure to send feedback on any issues you encounter through the upgrade process or after the upgrade completes. We appreciate Insiders helping us test out the upgrade from Windows Phone 8.1 to help ensure our customers have a great experience.
Last week, we reported that the "official" Windows 10 Mobile update will not be bundled with device specific firmware. Because of this, users can upgrade through the Release Preview ring and get the exact same update as they would if they waited for the "official" update.
Of course, nothing is finalized until that update actually rolls out to Windows Phone 8.1 users. We've seen issues before where Microsoft identified an important bug and had to hold off on releasing a new build in order to fix it. As it stands right now, though, it seems clear that the firm's plans are to roll out build 10586.122 to non-Insiders.
UPDATE: Brandon LeBlanc, Senior Program Manager at Microsoft for the Insider Program Team, has commented that they made no such implication and that this is "a bit of a stretch". He didn't give any indication of when the rollout might begin, given that it was due back in December.
Source: Windows Blog